The completion of oil and gas wells by gun perforating is well known in the art. A work string including one or more perforating guns is lowered into a well casing cemented into the well bore. The perforating guns are positioned adjacent to the formation to be perforated. The perforating guns are fired to penetrate the casing and cement and form perforations into the producing formation for recovery of the desired fluids. These perforating guns typically utilize shaped charges to form the perforations.
Perforating guns are made in numerous configurations. One common type of prior art perforating gun is illustrated in FIGS. 1A and 1B. This prior art gun assembly is described in more detail in U.S. Pat. No. 6,006,833, which is assigned to the assignee of the present invention and which is hereby incorporated by reference for all purposes. The loaded gun assembly 10 is assembled in a hollow steel carrier 12 having female threads 14 and 16 cut into each end. The carrier 12 has gun ports, or thinned wall areas often referred to as scallops, 20 aligned with shaped charges 22 carried in the carrier 12. A charge holder 24 provides a frame for assembling the shaped charges 22 and connecting them with detonating cord 26. When the charge holder 24 is inserted in the carrier 12, the charge holder 24 holds the shaped charges 22 in alignment with the scallops 20. In this prior art system, the shaped charges 22 and scallops 20 are arranged in a helical configuration. The charge holder 24 normally is connected to an upper alignment fixture 28 and a lower alignment fixture 30 for positioning the charge holder 24 in the carrier 12 and some type of alignment means for aligning the shaped charges 22 with the gun ports 20. A snap ring 32 or other retainer means may be provided, especially with lower alignment fixture 30, to keep the charge holder 24 from sliding out of the bottom of carrier 12 as it is handled.
The threaded ends 14, 16 of the perforating gun carrier 12 are normally used to connect a perforating gun 10 into a work string for lowering the guns into a well. The gun carrier 12 forms part of the mechanical structure of the work string and must support the loads normally encountered in lowering a work string into a well and in removing it from a well. Normally, high strength connectors are provided to connect a perforating gun into a work string. One typical connector 34 has male threaded portions 36 on both ends and may be referred to as a tandem connector. A tandem connector 34 may be used, for example, to couple two standard perforating guns together to form a longer gun assembly. Another typical connector 38 has one male threaded end 40 and one female threaded end 42 and may be referred to as a box x pin connector. These connectors 34 and 38 must support full work string loads. They must also include interior passageways 44 and 46 with charge assemblies 48 and 50 for explosive transfer from initiating devices or from and to other gun assemblies connected above and below the perforating gun 10. The interior passageways 44 and 46 may be of small diameter to hold the detonating cord 26, leaving a thick strong wall to carry the required loads.
The complete gun assembly 10 includes carrier 12 with charge holder 24, shaped charges 22, upper and lower alignment fixtures 28 and 30, a tandem connector 34 on one end and a box x pin connector 52 on the other end. This assembly 10 includes an extension of the detonating cord 26 carried in interior passageways 44 and 46 in connecters 34 and 38 respectively and forming part of charge assemblies 48 and 50. The outermost ends of the connectors carry booster charges 54 and 56 coupled to the detonating cord 26 for explosive transfer to and from adjacent guns or from initiating devices. The connectors 34 and 38 provide good mechanical support for retaining charge holder 24 within the gun carrier and provide a means for connecting a plurality of guns together into a work string. However, in addition to the carrier 12 itself, the assembly 10 requires the extra connectors 34 and 38, each of which requires fluid tight seals, and the process of assembling the parts is fairly complicated and time consuming.
Thus, it would be desirable to provide a simple, easily assembled perforating gun assembly.